The present invention relates to the sterilization arts. It finds particular application in conjunction with hydrogen peroxide vaporization systems used in connection with the sterilization of large enclosures, and their contents, and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable to other chemical vaporization systems such as peracetic acid vaporization systems.
Sterile enclosures are used by hospitals and laboratories for conducting tests in a microorganism-free environment. Processing equipment for pharmaceuticals and food, and freeze driers also include large enclosures which require sterilizing. Vaporized hydrogen peroxide is a particularly useful sterilant for these purposes because it is effective at low temperatures. Keeping the temperature of the enclosure near room temperature eliminates the potential for thermal degradation of associated equipment and items to be sterilized within the enclosure. In addition, hydrogen peroxide readily decomposes to water and oxygen, which, of course, are not harmful to the operator.
For effective sterilization, the hydrogen peroxide is maintained in the vapor state. Sterilization efficiency is significantly reduced by condensation. Many current hydrogen peroxide sterilizers inject a spray of hydrogen peroxide into a vacuum. The premier systems incorporate a single heated hydrogen peroxide vaporizer. A solution of about 35% hydrogen peroxide in water is injected into the vaporizer which heats it to form a vapor, without breaking it down to water and oxygen. A flow of air carries the vapor to the enclosure.
As the size of the enclosure increases, the demand for hydrogen peroxide is increased and the efficiency of the vaporization system becomes more significant. The capacity of the vaporizer is limited in a number of ways. First, the vaporization process creates a pressure drop, reducing the flow of air through the vaporizer. This increases the sterilization time and effectively limits the size of the enclosure to one which is capable of sterilization within an acceptable time period. Second, to maintain sterilization efficiency, the pressure at which the vapor is generated is limited to that at which the hydrogen peroxide is stable in the vapor state.
Further, large enclosures create problems themselves. Temperature differences throughout the chamber require different concentrations of the sterilant to compensate for condensation on cooler surfaces. Items within the enclosure require different concentrations of sterilant for optimum exposure because of their relative absorbencies. Pumping the vapor to more distant regions within the enclosure increases the extent of condensation within the vapor supply lines, reducing effectiveness.
One solution was to increase the size of the vaporizer and the injection rate of hydrogen peroxide into the vaporizer. Although helpful, the larger vaporizer still suffers from concentration variations and condensation concerns.
The present invention provides a new and improved vaporization system which overcomes the above referenced problems and others.